Playground for Go Generate Using Proto Files⌗

This is a small application to demonstrate how to use go generate to compile proto files into Go code.

Note: all code is available on GitHub here.

Go Generate⌗

The original blog post by Rob Pike is well worth a read. At the bottom, Rob says

Please use go generate creatively. It’s there to encourage experimentation.

This is one such experimentation.

Protobuf, gPRC, and Generating Code⌗

If you are unfamiliar with Protocol Buffers and gRPC, those linked resources are worth a read. However, just know that Protobuf is a language spec that allows you to define abstract API contracts within generated code stubs. Your application needs to implement these interfaces for clients to consume. The benefit is that both client and server consume and fulfill requests using the same base .proto file and its generated code, allowing for incredible type safety.

Protoc Hassles⌗

Go developers using Protobuf for a few years are probably familiar with the protoc binary used and the protoc-gen-go plugin. This is the tool we use to generate Go stubs from proto files. Protoc commands can be provided via scripts, in Dockerfiles, or ran directly to ensure that code is generated and types are accessible to your application. This decouples the proto compilation step from your app compilation. If you want to couple the two together, go generate may be your answer.

Go Generate (again)⌗

The go generate command searches through your Go files for the //go:generate comment (notice no space between the slashes and go). Adding this tag tells the Go toolchain to run whatever shell commends follow.

Tagging for Go Generate⌗

You can see here that main.go has two go generate tags.

//go:generate protoc --go_out=. --go-grpc_out=. proto/helloapis/messages.proto
//go:generate protoc --go_out=. --go-grpc_out=. proto/helloapis/services.proto

These two tags will compile protos found in proto/helloapis and move them into the directory indicated by their package name. In this instance, that directory is gen/helloapis/v1.

Building the Application⌗

Attemping to run go build . before compiling the protos will fail.

❯ go build . client/client.go:6:2: package playgen/gen/helloapis/v1 is not in std (/snap/go/10630/src/playgen/gen/helloapis/v1)

To resolve this, run go generate ./....

❯ go generate ./…

Notice that a new gen directory is in the repo root.

❯ ls
build  client  docker-compose.yaml  gen  go.mod  go.sum  main.go  proto  README.md  server

The application is now buildable and runnable!

❯ go build .
❯ ls
build  client  docker-compose.yaml  gen  go.mod  go.sum  main.go  playgen  proto  README.md  server
❯ ./playgen
Hello, vim-go!